1. Field of the Invention
The present invention relates to an optical pickup having a liquid crystal panel for correcting an aberration.
2. Description of Related Art
As to an optical pickup, there is a known technique of mounting a liquid crystal element such as a liquid crystal panel thereon in order to correct various aberrations caused by inclination of an optical disc, a difference in thickness between different optical discs such as a CD and a DVD and so on. For instance, in the case of the optical pickup described in Japanese Patent Application Laid-Open No. 10-289465, a so-called tilt correction to the inclination of the disc is performed by providing wavefront aberration correcting means comprised of the liquid crystal panel on a light path between a laser source and an objective lens. The liquid crystal panel as the wavefront aberration correcting means has its electrodes divided into forms corresponding to wavefront aberration distribution caused by a tilt angle of the optical disc. Different voltages are applied to the divided portions to give different refractive indexes, and a phase difference is given to a laser beam so as to correct the wavefront aberration. To the liquid crystal panel, the voltage corresponding to a direction and an amount of the aberration to be corrected is applied in reference to a predetermined bias voltage. However, there is a problem that reproduction performance deteriorates depending on a set value of the bias voltage.
Japanese Patent Application Laid-Open No. 2001-273663 discloses a method of switching the bias voltage applied to the liquid crystal element in an aberration correction apparatus using the liquid crystal element.